Time-to-contact: "auditory looming" (John Neuhof) and, off to one side slightly, "acoustic tau"
One point of studying many of these phenomena is to observe how profoundly non-linear perception is - it's not really about accurately observing 'the truth' of a situation, it's about observing 'MY truth'. Plato was right after all... Dr. Peter Lennox School of Technology, Faculty of Arts, Design and Technology University of Derby, UK e: p.len...@derby.ac.uk t: 01332 593155 -----Original Message----- From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On Behalf Of Eric Carmichel Sent: 02 April 2013 22:51 To: sursound@music.vt.edu Subject: Re: [Sursound] Anthropometrics, Loudspeakers, & Vision Hello Etienne and all Sursound Readers, Many thanks for your response, insight, and “food for thought”. You brought up interesting points which, in turn, prompted me to dig deeper into Ecological Psychology (referring to the Gibsonian school). There’s certainly something to be said for choosing the “right” information versus ability to detect or pick up additional information. In fact, this could get to the heart of some of my initial thoughts regarding hearing research (and my initial interest in Ambisonics). As you may know from prior diatribes and posts, I have interests in cochlear implant research and spatial hearing. It probably comes as zero surprise that an array of 22 electrodes used to innervate the auditory nerve provides, at best, impoverished input to the brain (especially when compared to the input provided by the approx. 3500 inner hair cells of normal-hearing listeners). When electric hearing is combined with acoustic hearing (hearing aid or not), we might surmise that the low-frequency (acoustic) energy simply adds to the amount of information received. For normal-hearing and impaired listeners alike, the low-frequency energy by itself provides very little usable information. For example, low-pass filtered speech (f3 = 200 Hz, high-order filter) is quite difficult to understand. In fact, f0 for women is above 200 Hz, so little speech information resides at the very low lows. Electric (cochlear implant) hearing alone provides reasonably good speech comprehension scores when speech stimuli are presented in a quiet environment (+20 dB or better SNR). Scores obtained from 5-word sentences could range from 50 – 90 percent correct (I don’t have an exact reference at hand, but I believe this is a good estimate). When electric hearing is augmented with the below-200 Hz acoustic stimulus, speech scores improve by a big jump. Furthermore, speech comprehension ability in reverberant environments improves. One might be inclined to conclude that when the sensory input is impoverished, any additional input is welcomed and quickly used to fill in any missing information gaps or resolve ambiguities. But the synergistic combination of electric and acoustic hearing suggests, at least to me, something beyond “additional” information is at work. Research regarding electric-acoustic stimulation (EAS) has led to exciting results and interesting discussions, but the background noise and reverbation used in many studies are often of the artificially-generated (pink or white noise maskers) and one-dimensional or mono reverb nature. Sursound Digest readers probably recall the discussion I initiated regarding multi-channel subwoofers and identifying sound-source direction (at least in free-field) for very low frequency sounds. My interest and concern for presenting accurate low-frequency and realistic sound source direction wasn’t about measuring localization ability for very low-frequency sounds: My interest was to build a periphonic system for evaluating REAL-WORLD low-frequency sounds’ contribution to or detraction from EAS listening. Needless to say, real-world sounds don’t come from a single subwoofer or direction. Whether we can determine direction isn’t the important part, but the subtle (and perhaps subconscious) aspects of real-world listening do matter. My take or concern over “realism” versus artificially produced stimuli isn’t one of difficulty; in fact, I’d state that many artificial and monaural noises (dichotic or diotic presentation) mixed with speech present more difficult listening conditions than what we encounter in the real world. The problem is one of learning what is “real” and useful. As an analogy, being able to ride a unicycle (arguably difficult) doesn’t guarantee one’s success or ability to ride a bicycle. It may be easier to ride a bike, but there are also more ways to fall or crash at high speed, so the need to maneuver a bike and learn the rules of the road are more important for safety. Learning, success, or attending to a difficult listening task in the laboratory doesn’t guarantee user success in the cacophony of real-world stimuli. To date, I’m not aware of studies where real-world stimuli and scenarios have been used to study the efficacy of EAS listening. It is entirely possible that the addition of low-frequency energy, whether a part of speech signal or not, helps users choose the “right” information. In the real world, there is a lot of multi-sensory noise. For normal-hearing listeners, segregating an auditory signal from noise is accomplished, in part, by perceived spatial separation. This is equally important for those involved with the recording arts: Spatially separating a pair of shakers from a hi-hat is most often accomplished via panning. With speech, we also face informational masking as well as energy masking. So, adding more “speech” information (aside from level to improve SNR) isn’t as important as our ability to choose information deemed important to the task at hand. We do learn from experience what is “true” or “correct” and is why we can learn to localize with fake pinnae or even develop localization ability with ONE ear (animal research supports this). Cochlear implant recipients need time, too, to make use of their “new” sense of hearing. Another area I would be interested in investigating is time-to-contact as it applies to hearing (Gibson was mostly involved with vision), and how binaural implantation might improve a listeners sense of safety in “three dimensional” space where there are multiple, moving, sound sources. Such studies under headphones are very realistic. As you wrote, “One of the characteristics in Gibson’s ecological approach that has been adopted by the VR field is the idea that perceptions are confirmed as true through ‘successful action in the environment’. Tilting one’s head can be considered action in the environment, and if the spatiality of the sounds heard correlate then that action can be considered successful. So head movements help to confirm that what is being perceived is correct.” I very much agree with what you wrote. Adding to this, avoiding collision is certainly a more successful action than identifying location to the nearest nth of a degree. Thanks for taking time to read. I always look forward to the Sursound Digest regardless of topic. Best always, Eric C. -------------- next part -------------- An HTML attachment was scrubbed... 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